CN111149237B - Porous separator and electrochemical device comprising same - Google Patents

Abstract

According to the present invention, there is provided a porous separator having a porous layer comprising: a plurality of plate-shaped inorganic particles; The first binder polymer of the plate-shaped inorganic particles. The present invention also provides an electrochemical device comprising the porous separator.

Description

Porous separator and electrochemical device incorporating same

technical field

This application claims Korean Patent Application No. 10-2017-0173537 filed with the Korean Intellectual Property Office on December 15, 2017 and Korean Patent Application No. 10-2018-0162329 filed with the Korean Intellectual Property Office on December 14, 2018 The entire content of said patent application is incorporated herein by reference.

The present invention relates to a porous separator and an electrochemical device including the same, and to a porous separator capable of preventing lithium ion dendrites and having improved high-temperature safety due to excellent thermal properties, and an electrochemical device including the same.

Background technique

Recently, there has been a growing interest in energy storage technologies. As applications expand to energy sources for cell phones, camcorders, and notebook PCs, and furthermore, to electric vehicles, research and development efforts on electrochemical devices are becoming more and more concrete. In these respects, electrochemical devices are the field receiving the most attention, and among them, the development of secondary batteries capable of charging and discharging has been the focus of attention, and the development of such batteries has been carried out to research and develop methods for improving capacity density and Design of new electrodes and batteries for specific energy.

Among the currently used secondary batteries, lithium secondary batteries developed in the early 1990s are known for their higher The advantages of operating voltage and significantly higher energy density have attracted attention. However, such lithium ion batteries have safety problems such as fire and explosion due to the use of an organic electrolyte, and have disadvantages of complicated manufacture.

The recent lithium-ion polymer battery has been considered as one of the next-generation batteries by improving these weaknesses of lithium-ion batteries, however, its battery capacity is still relatively low compared to lithium-ion batteries, and in particular, discharge at low temperatures The capacity is insufficient, and there is an urgent need to improve it.

Electrochemical devices such as those described above have been produced by many companies, but their safety profiles vary widely. For these electrochemical devices, it is very important to evaluate safety and ensure safety. The most important consideration is not to cause harm to the user in the event of a malfunction of the electrochemical device, and for this reason, fire, smoke generation, etc. in the electrochemical device are strictly controlled in the safety requirements. In terms of the safety characteristics of electrochemical devices, there is a great fear of explosion when thermal runaway occurs due to overheating of electrochemical devices or a separator is penetrated. In particular, polyolefin-based porous substrates commonly used as separators for electrochemical devices show extreme thermal shrinkage behavior at temperatures above 100°C due to material properties and characteristics of manufacturing processes involving stretching, resulting in positive electrode short circuit to positive.

In order to solve such safety problems of electrochemical devices, there has been proposed a method of forming an electrochemical device by coating an excess of a mixture of inorganic particles and a binder polymer on at least one surface of a polyolefin-based porous substrate having many pores. Porous organic-inorganic coated separator.

However, the porous layer herein may have coating defects on the surface due to cracks that occur during the preparation process such as the drying process. As a result, when a secondary battery is assembled or the battery is used, the organic/inorganic composite porous layer may be easily detached from the polyolefin-based porous substrate, and this leads to a decrease in battery safety. In addition, a slurry for forming a porous layer coated on a polyolefin-based porous substrate to form a porous layer increases the bulk density of particles during drying, resulting in the generation of a portion filled at a high density, which causes a problem of decreased air permeability .

In addition, the heavy metal components inevitably mixed in the battery electrode plate preparation process and raw material preparation process are oxidized and reduced during the battery activation process while being precipitated on the surface of the negative electrode, and the resulting metal lithium needle crystals (dendrites) This causes a micro-short circuit in the positive or negative electrode, which causes the battery voltage to drop.

Therefore, there remains a need for further improved separators that can contribute to battery stability, as higher and higher levels of stability are required due to the nature of the battery industry.

[Prior art literature]

(Patent Document 1) Korean Patent Application Publication No. 10-2017-0053448

Contents of the invention

【technical problem】

Accordingly, an aspect of the present invention provides a porous separator capable of preventing a short circuit phenomenon between a positive electrode and a negative electrode caused by dendrite growth and having improved high-temperature safety due to excellent thermal properties, and a battery including the porous separator. chemical device.

【Technical solutions】

According to one aspect of the present invention, a porous separator of the following embodiments is provided.

The first embodiment relates to a porous separator comprising a porous layer comprising: a plurality of plate-shaped inorganic particles; A first binder polymer for the inorganic particles.

A second embodiment relates to the porous separator of the first embodiment, further comprising a porous coating on at least one surface of the porous layer and comprising: a plurality of spherical inorganic particles; The second binder polymer is used to connect and fix the spherical inorganic particles on a part or the whole surface of the spherical inorganic particles.

A third embodiment relates to the porous separator according to the first embodiment or the second embodiment, wherein the plate-shaped inorganic particles have an aspect ratio of 5 to 100.

The fourth embodiment relates to the porous separator according to any one of the first to third embodiments, wherein the plate-shaped inorganic particles include alumina, silica, zirconia, titania, magnesia, Cerium, yttrium oxide, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide, or a mixture of two or more thereof.

A fifth embodiment relates to the porous separator according to any one of the second to fourth embodiments, wherein the spherical inorganic particles have an aspect ratio of 1 to 2.

A sixth embodiment relates to the porous separator according to any one of the second to fifth embodiments, wherein the spherical inorganic particles contain alumina, silica, or a mixture thereof.

A seventh embodiment relates to the porous separator according to any one of the first to sixth embodiments, wherein the porous layer further contains spherical inorganic particles.

According to another aspect of the present invention, electrochemical devices of the following embodiments are provided.

The eighth embodiment relates to an electrochemical device, which includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is any one of the first to seventh embodiments The porous diaphragm.

The ninth embodiment relates to the electrochemical device according to the eighth embodiment, which is a lithium secondary battery.

【Beneficial effect】

According to one embodiment of the present invention, the path between the positive electrode/negative electrode, the so-called tortuosity, can be increased by providing the base layer containing plate-shaped inorganic particles, and even when dendrites are generated in the battery, the corresponding dendrites are It is difficult to reach the positive electrode from the negative electrode, and the reliability regarding dendrite short circuit can be further improved.

In addition, since the porous separator according to one embodiment of the present invention does not have a porous polymer substrate, the effect of cost reduction can be obtained, a uniform porous separator can be obtained by controlling the pore size and porosity of the entire separator, and it is possible to obtain a uniform porous separator by reducing the size of the separator. thickness to reduce weight. In addition, since there is no phenomenon such as thermal shrinkage even when exposed to a high temperature of 120° C. or higher, an advantage of improved safety can be obtained.

Description of drawings

FIG. 1 is a schematic diagram illustrating the degree of tortuosity in a porous layer formed of inorganic particles.

Fig. 2 is a schematic diagram illustrating the degree of tortuosity in a porous layer formed of spherical inorganic particles.

Fig. 3 is a schematic diagram illustrating the degree of tortuosity in a porous layer formed of plate-like inorganic particles.

Figure 4 is a schematic diagram of a porous membrane according to one embodiment of the present invention.

Figure 5 is a schematic diagram of a porous membrane according to one embodiment of the present invention.

Figure 6 is a schematic diagram of a porous membrane according to one embodiment of the present invention.

FIG. 7 is a graph presenting the evaluation results of life characteristics of Example 1, Example 2, and Comparative Example 1. FIG.

detailed description

Hereinafter, the present invention will be described in detail. The terms or words used in the specification and claims should not be construed as limited to the ordinary meaning and the meaning in the dictionary, but should be based on the principle of allowing the inventor to properly define the concept of the term to best explain the present invention. The meaning and concept of the technical concept of the present disclosure will be explained.

A porous separator according to one aspect of the present invention has a porous layer including: a plurality of plate-shaped inorganic particles; binder polymer.

As described below, the porous separator of the present invention can function as a separator by being disposed between a positive electrode and a negative electrode. Therefore, the porous separator can correspond to a porous separator (separation membrane, separator), and can also correspond to an organic-inorganic composite since an organic material and an inorganic material are mixed in terms of constituent components.

Such organic-inorganic composites are formed only of inorganic materials and binder polymers without porous polymer substrates such as polyolefins, therefore, compared to conventional separators formed of porous polymer substrates, even when exposed to The separator will not heat shrink at high temperatures above 120°C, and will not decompose or be damaged even when the temperature rises to near the melting point of the polymer substrate, so the possibility of short circuiting between the positive and negative electrodes can be fundamentally prevented performance, and can reduce weight by reducing the thickness of the diaphragm.

Meanwhile, in order to safely use an electrochemical device such as a secondary battery for a long time, it is necessary to suppress the formation of dendrites by foreign metal ions in the battery generated during charge and discharge through reduction on the surface of the negative electrode and the formation of dendrites caused by such dendrites. internal short circuit of the battery. In addition, from the standpoint of battery manufacturing quality, the defect rate during battery manufacturing increases due to dendrites generated by the reduction of such metal ions in charge and discharge in the battery manufacturing process. In addition, when the dendrites generated during the manufacturing process electrically connect the positive and negative electrodes by external pressure or vibration, there may be problems with the safety and stability of the battery during use, and the metal ions additionally generated during the use of the battery The reduction of α also leads to the formation of dendrites, which greatly impairs the safety and stability of the battery. Therefore, in such lithium secondary batteries, it is necessary to suppress the formation and growth of dendrites that may electrically connect the positive and negative electrodes inside the battery.

When using a porous organic-inorganic layer with inorganic particles as a separator, the pores of such a porous organic-inorganic layer, that is, the spaces and paths between the inorganic particles may have an effect on dendrite growth and the electrical short circuit phenomenon between the positive and negative electrodes. Significantly affected. When the time required for metal ions to pass through the separator and transport to the negative electrode increases, or even when metal ions pass through the separator and dendrites are precipitated on the surface of the negative electrode, when the path to the opposite positive electrode is complicated due to precipitation and growth or As the time taken increases, the growth of dendrites resulting from the reduction of metal ions and precipitation on the surface of the negative electrode may be inhibited or delayed.

The movement path affecting the precipitation and growth of foreign metal ions in such a porous organic-inorganic layer with inorganic particles can be explained by the tortuosity.

Tortuosity is a value that quantifies how curved or twisted a curve is, and is often used in general when describing diffusion that occurs in porous materials. When referring to FIG. 1 , the tortuosity τ can be defined as follows.

此处，△ι：实际移动长度，△χ：单位长度。

Here, Δι: actual moving length, Δχ: unit length.

In other words, even when the thickness of the porous layer formed by a plurality of particles (1) corresponds to Δχ, the time to pass through the pores (2) of the porous layer and pass from one side to the other is different from the actual moving distance Δ ι is directly proportional.

When referring to FIGS. 2 and 3 , it can be seen that in a porous separator with a binder polymer and inorganic particles, the actual moving distance may vary significantly depending on the type of inorganic particles. Compared with the plate-shaped inorganic particles (5) in FIG. 3, the spherical inorganic particles (3) in FIG. The length of travel passes from one side to the opposite side. From this, it can be seen that when the inorganic particle shape of the porous separator is plate-like, it is difficult for dendrites formed on the surface of the negative electrode to grow, pass through the pores of the separator, and connect to the positive electrode side due to the increase in the travel length compared to when they are spherical. And take a longer time, so the dendrite growth and the resulting short circuit phenomenon is suppressed.

Therefore, the present invention provides a porous separator including a porous layer provided with plate-shaped inorganic particles.

When referring to Fig. 4, a porous diaphragm (100) according to one embodiment of the present invention has a porous layer (10) comprising: a plurality of plate-shaped inorganic particles (11); A first binder polymer (not shown) on a part or all of the surface of the plate-shaped inorganic particles (11) to connect and fix the plate-shaped inorganic particles.

In addition, according to one embodiment of the present invention, there may be further provided a porous coating, which is located on at least one surface of the porous layer and includes: a plurality of spherical inorganic particles; A second binder polymer to connect and fix the spherical inorganic particles.

Compared with the case where the porous separator includes a porous layer formed of plate-like inorganic particles, when a porous coating layer including spherical inorganic particles is further provided, lithium ions from the electrodes can be uniformly diffused and passed through the separator. Here, when spherical inorganic particles are uniformly dispersed into the coating, lithium ions can pass through the separator more uniformly. When the coating is formed by uniformly dispersing spherical inorganic particles, the pores of the coating are also uniformly distributed, and therefore, lithium ions can enter the uniformly dispersed pores. Specifically, lithium ions can be plated on the electrode by passing through the porous layer of plate-shaped inorganic particles with difficulty, and then uniformly passing through the porous coating of spherical inorganic particles on the opposite side. In other words, the spherical inorganic particles are used to make the transmission and distribution of lithium ions uniform, while the plate-shaped inorganic particles can reduce the short circuit phenomenon of the battery by making it difficult for lithium ions to pass through.

When referring to FIG. 5, a porous membrane (200) according to one embodiment of the present invention has a porous layer (10) comprising: a plurality of plate-shaped inorganic particles (11), and A first binder polymer (not shown) to connect and fix the plate-shaped inorganic particles on a part or all of the surface; and a porous coating (20) located on one surface of the base porous layer and comprising: A plurality of spherical inorganic particles (21), and a second binder polymer (not shown) positioned on a part or all of the surfaces of the spherical inorganic particles (21) to connect and fix the spherical inorganic particles.

In addition, the porous separator (300) according to one embodiment of the present invention shown in FIG. 6 has: a porous layer 10 including a plurality of plate-shaped inorganic particles (11), and A first binder polymer (not shown) to connect and fix the plate-shaped inorganic particles on a part or all of the surface; a porous coating (20), which is located on one surface of the basic porous layer, and contains multiple a spherical inorganic particle (21), and a second binder polymer (not shown) positioned on a part or all of the surface of the spherical inorganic particle (21) to connect and fix the spherical inorganic particle; and a porous coating layer (30), which is located on the other surface of the basic porous layer, and contains a plurality of spherical inorganic particles (31), and is located on a part or all of the surface of the spherical inorganic particles (31) to connect and fix the The second binder polymer (not shown) of the spherical inorganic particles.

According to one embodiment of the present invention, the inorganic particles in the porous layer may be formed only of plate-shaped inorganic particles, or may have an amount of 50% by weight or more and specifically 50% by weight to 50% by weight relative to the total weight of the inorganic particles in the porous layer. 90% by weight of plate-shaped inorganic particles. In the latter case, spherical inorganic particles may be further contained as inorganic particles of the porous layer.

In addition, according to one embodiment of the present invention, the inorganic particles in the porous coating may be formed only of spherical inorganic particles, or may have an amount of 50% by weight or more and specifically 50% by weight relative to the total weight of the inorganic particles of the porous coating. to 90% by weight of spherical inorganic particles. In the latter case, plate-shaped inorganic particles may be further contained as inorganic particles of the porous coating layer.

Non-limiting examples of plate-like inorganic particles may include alumina, silica, zirconia, titania, magnesia, ceria, yttrium oxide, zinc oxide, iron oxide, barium oxide, titanium oxide, alumina-silica composite oxides, or a mixture of two or more of them.

Non-limiting examples of the spherical inorganic particles may include highly dielectric inorganic particles having a dielectric constant of 5 or more, specifically 10 or more, inorganic particles having lithium ion transport capability, or a mixture thereof.

Non-limiting examples of inorganic particles having a dielectric constant of 5 or more may include BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT), PB (Mg ₃ Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), hafnium dioxide (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O _3. Al ₂ O ₃ , TiO ₂ , SiC, AlO(OH), Al ₂ O ₃ ·H ₂ O or mixtures thereof.

In addition, the inorganic particle having lithium ion transport ability refers to an inorganic particle containing lithium element but having a function of moving lithium ion instead of storing lithium, and a non-limiting example of the inorganic particle having lithium ion transport ability may include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li _x Al _{y Tiz} (PO ₄ ) ₃ , 0 <x<2, 0<y<1, 0<z<3), (LiAlTiP) _x O _y series glass (0<x<4, 0<y<13) such as 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ , lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0<x <4, 0<y<1, 0<z<1, 0<w<5) such as Li _3.25 Ge _0.25 P _0.75 S ₄ , lithium nitride (Li _x N _y , 0<x<4, 0<y< 2) Such as Li ₃ N, SiS ₂ series glasses (Li _x Si _y S _z , 0<x<3, 0<y<2, 0<z<4) such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ , P ₂ S ₅ series glasses (Li _x P _y S _z , 0<x<3, 0<y<3, 0<z<7) such as LiI-Li ₂ SP ₂ S ₅ , or their mixtures.

The aspect ratio of the plate-shaped inorganic particles may be 5 to 100, specifically 50 to 100.

The aspect ratio of the spherical inorganic particles may be 1 to 2, specifically 1 to 1.5.

Here, the aspect ratio refers to the average value of the ratio of the length in the major axis direction to the length in the minor axis direction (length in the major axis direction/length in the minor axis direction) of the inorganic particles.

The aspect ratio of the inorganic particles, that is, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction, can be obtained by, for example, image analysis of photographs taken with a scanning electron microscope. In addition, the aspect ratio of inorganic particles can also be obtained by image analysis of photographs taken by SEM.

In the porous separator according to one aspect of the present invention, a polymer having a glass transition temperature (T _g ) of -200°C to 200°C can be used as the first binder polymer and the second binder polymer used. This is because the mechanical properties such as flexibility and elasticity of the final porous membrane can be improved. Such a binder polymer contributes to preventing deterioration of the mechanical properties of the porous separator by reliably exerting the link of the binder and stably fixing the inorganic particles.

In addition, the first binder polymer and the second binder polymer do not necessarily have ion conductivity, but when polymers having ion conductivity are used, the performance of the electrochemical device can be further improved. Therefore, a polymer having a high dielectric constant can be used as the first binder polymer and the second binder polymer. In fact, the degree of dissociation of salt in electrolyte depends on the dielectric constant of the electrolyte solvent, therefore, the degree of dissociation of salt in electrolyte can be enhanced with the increase of the dielectric constant of the binder polymer. As the dielectric constant of such a first binder polymer and a second binder polymer, a range of 1.0 to 100 (measurement frequency=1 kHz) can be used, and in particular, 10 or more can be used.

In addition to the above functions, the first binder polymer and the second binder polymer may also have a property of exhibiting a high degree of swelling of the electrolyte by gelling when impregnated with the liquid electrolyte. Thus, the solubility parameter of the binder polymer, ie the Hildebrand solubility parameter, is in the range of 15 MPa ^1/2 to 45 MPa ^1/2 or 15 MPa ^1/2 to 25 MPa ^1/2 and 30 MPa ^1/2 to 45 MPa ^1/2 . Therefore, hydrophilic polymers with more polar functional groups can be used to a greater extent than hydrophobic polymers such as polyolefins. This is because, when the solubility parameter is less than 15 MPa ^1/2 or greater than 45 MPa ^1/2 , it is difficult to perform swelling by a conventional liquid electrolyte for batteries.

In the porous separator, the inorganic particles are bound to each other by the first binder polymer and the second binder polymer while being filled and in contact with each other, as a result, interstitial volumes are formed between the inorganic particles, and the gaps between the inorganic particles The volume becomes empty space forming pores.

In other words, the first binder polymer and the second binder polymer adhere to the inorganic particles so that the inorganic particles can remain bonded to each other, for example, the first binder polymer and the second binder polymer are connected And fixed inorganic particles. In addition, the pores of the porous separator are pores formed by interstitial volumes between inorganic particles that become empty spaces, and this is a space defined by inorganic particles substantially joined by inorganic particles in a close-packed or close-packed structure.

As such a first binder polymer and a second binder polymer, those satisfying the above weight average molecular weight and generally used in the art may be used without limitation. Examples thereof may include polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyimide, polymethyl methacrylate, polybutyl acrylate , polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, Cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc., but not limited thereto.

Relative to the total weight of the porous layer, the weight of the first binder polymer may be 0.1% by weight to 30% by weight, specifically 0.3% by weight to 25% by weight, and more specifically 0.5% by weight to 20% by weight. weight%.

In addition, relative to the total weight of the porous coating layer, the weight of the second binder polymer may be 0.1% by weight to 30% by weight, specifically 0.3% by weight to 25% by weight, and more specifically 0.5% by weight % to 20% by weight.

When the weights of the first binder polymer and the second binder polymer each satisfy the range, the pore size and porosity due to excess binder polymer present in the formed pores of the porous separator can be prevented Reduced problems, and the inorganic particles can be stably fixed by the binder polymer without detachment during the preparation of the porous separator, or during the storage or handling of the electrochemical device having the porous separator.

The porous separator according to one aspect of the present invention may contain other additives in addition to the above-mentioned inorganic particles and binder polymer.

The porous separator according to one embodiment of the present invention can be prepared by the following steps: first, prepare a base layer composition having plate-shaped inorganic particles and a first binder polymer, and apply such a composition on the release substrate. On one surface, the resultant is dried and the release substrate is removed. Alternatively, the composition for forming a porous separator is directly coated on one surface of an electrode layer such as a positive electrode or a negative electrode, and then dried to prepare an electrode-porous layer composite directly bonded to the electrode layer.

First, the base layer composition may be prepared by dissolving the first binder polymer in a solvent, adding plate-shaped inorganic particles thereto, and dispersing the resultant. The plate-shaped inorganic particles may be added in a state of being pulverized in advance to have a certain average particle diameter, or after the inorganic particles are added to the solution of the binder polymer, the inorganic particles may be controlled to have a certain average particle diameter by using a ball milling method or the like. crushed and dispersed at the same time.

There is no particular limitation on the method of coating the base layer composition on the release substrate or the electrode layer, however, preferably, slit coating, comma coating, curtain coating, microgravure coating, spin coating, Roll coating, dip coating, etc.

Slot coating is a method of coating a composition supplied through a slot die on the entire surface of a substrate, and the coating thickness can be adjusted according to the flow rate supplied from a metering pump. In addition, dip coating is a method of coating by dipping the substrate into a tank containing the composition, and the coating thickness can be adjusted according to the composition concentration and the speed at which the substrate is taken out of the composition tank, and for more precise To accurately adjust the coating thickness, post-measurement can be performed after dipping by a Meyer bar or the like.

The porous layer can be prepared by drying the release substrate coated with the composition for forming a porous separator using a drier such as an oven at a temperature of, for example, 90°C to 150°C, and then removing the release substrate. As such a release base material, a glass plate, a polyethylene film, a polyester film, etc. can be used, but the release base material is not limited thereto. Alternatively, the surface of the release substrate may be surface-modified by corona treatment (eg, treatment at a voltage of 0.5 kV to 1.5 kV for 10 seconds to 30 seconds) or the like.

Alternatively, when the base layer composition is directly coated on the electrode layer, drying may be performed in the same manner to prepare an electrode-porous layer composite bonded to the electrode layer.

The coating thickness of the porous layer formed by coating in the above-mentioned manner may be 5 μm to 20 μm.

Next, a porous coating layer may be additionally formed after coating the porous coating composition on at least one surface of the prepared porous layer and drying the resultant.

The porous coating composition can be prepared by dissolving the second binder polymer in a solvent, adding spherical inorganic particles thereto, and dispersing the resultant, and for methods other than this, the preparation can be used in the same manner. Method for base layer composition.

When the porous coating is formed on both surfaces of the porous layer, the dip coating method may be used, and when formed on only one surface, other various coating methods described above may be used.

The coating thickness of the porous coating layer formed by coating in the above-mentioned manner may be 5 μm to 20 μm.

In the present invention, porosity is measured using a capillary flow porosimeter device from Porous Materials Inc. .

According to one embodiment of the present invention, regarding the existence type of the plate-shaped inorganic particles in the porous layer, it is preferable that the plate surface is substantially parallel to the surface of the porous layer.

An electrochemical device according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the separator is the above-described porous separator according to one embodiment of the present invention.

Such electrochemical devices include all devices that perform electrochemical reactions, and specific examples thereof may include all types of primary batteries, secondary batteries, fuel cells, solar cells, capacitors such as supercapacitor devices, and the like. In particular, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, lithium ion polymer secondary batteries, and the like are preferable.

Both positive and negative electrodes used with the porous separator of the present invention are not particularly limited, and can be prepared in the form of bonding electrode active materials on electrode collectors according to common methods known in the art. Non-limiting examples of the positive electrode active material of the electrode active material can include conventional positive electrode active materials that can be used in the positive electrode of existing electrochemical devices, particularly preferably using lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide substances, or lithium composite oxides combining these. Non-limiting examples of negative electrode active materials may include conventional negative electrode active materials that can be used in negative electrodes of existing electrochemical devices, and particularly preferably lithium metal or lithium alloys, or lithium adsorbent materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons class etc. Non-limiting examples of positive electrode current collectors may include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative electrode current collectors may include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

The electrolyte solution that can be used in the electrochemical device of the present invention is a salt having a structure such as A ⁺ B ⁻ , and may contain a salt in which A ⁺ is composed of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or ions formed by combination and B ^- contains anions such as PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N( CF ₃ SO ₂ ) ₂ ^- , C(CF ₂ SO ₂ ) ₃ ^- or ions formed by a combination thereof, and the salt is dissolved or dissociated in an environment containing propylene carbonate (PC), ethylene carbonate (EC), Diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl In an organic solvent of phenyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone (g-butyrolactone) or a mixture thereof, but the salt is not limited thereto.

Depending on the manufacturing process and the desired properties of the final product, the electrolyte can be injected at an appropriate stage in the battery manufacturing process. In other words, the electrolyte can be used at a stage before battery assembly or at the final stage of battery assembly.

Hereinafter, the present invention will be described in detail with reference to Examples to specifically describe the present invention. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention is not construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those of ordinary skill in the art.

[Example 1]

<Preparation of Porous Separator 1>

After mixing PVdF-HFP polymer binder (Arkema Group, LBG grade) and inorganic particles (alumina, TCERA Co., Ltd., NW-710 grade) at a ratio of 9:1, the resultant was mixed with An N-methyl-2-pyrrolidone (NMP) solvent was mixed at a solid concentration of 40% to prepare a coating liquid.

On the polyethylene terephthalate (PET) film (SKC, RX12G50 μm) that the intensity corona of 0.7Kw has been treated on the surface, use applicator to coat the above-mentioned prepared coating solution, and the resultant is in Dry in a Mathis oven at 130 °C for 5 min to prepare a PET film coated with a porous separator with a thickness of 100 μm.

The PET film coated with the porous separator was rolled in a rolling machine (calender, CIS Co., Ltd., CLP-2025H) to prepare a porous separator with a thickness of 20 μm, and then peeled off.

<Preparation of Porous Separator 2>

A separator having a thickness of 10 μm was prepared in the same manner as the preparation of the porous separator except for using spherical alumina (Dae Han Ceramics Co., Ltd., SRA-05S).

<Manufacture of Lithium Secondary Batteries>

96.7 parts by weight of LiCoO ₂ used as a positive electrode active material, 1.3 parts by weight of graphite used as a conductive material, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) used as a binder were mixed to prepare a positive electrode mixture. A cathode mixture slurry was prepared by dispersing the obtained cathode mixture into 1-methyl-2-pyrrolidone used as a solvent. This slurry was coated on both surfaces of an aluminum foil having a thickness of 20 μm, dried and compressed to prepare a positive electrode.

As the negative electrode, a Li metal electrode (Honjo Metal Co., Ltd., Japan) in which a 100% Li metal layer was formed with a thickness of 20 μm on a copper foil current collector was used.

Obtained by dissolving LiPF ₆ at a concentration of 1.0M in a composition of 1:2:1 (volume ratio) and mixing ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) In an organic solvent, and with respect to 100 parts by weight of the organic solvent, 2 parts by weight of vinylene carbonate was dissolved to prepare a non-aqueous electrolytic solution.

A porous separator was provided between the positive electrode and the negative electrode prepared above, and an electrolytic solution was injected to manufacture a button cell type lithium secondary battery.

[Example 2]

In the same manner as in Example 1, except that the separator prepared in the preparation of the porous diaphragm 1 was placed in the middle and the two sheets of the diaphragm prepared in the preparation of the porous diaphragm 2 were disposed above and below to obtain a three-layer structure. Lithium secondary batteries were produced by the method.

[Comparative example 1]

A lithium secondary battery was fabricated in the same manner as in Example 1 except that a CSP20 product manufactured by Optodot was used as the porous separator.

Physical property evaluation

Evaluation of life characteristics

The lithium secondary batteries of Examples 1 and 2 and Comparative Example 1 were each subjected to CC charging at a constant current (CC) of 0.2C to 4.25V using a small battery cycler device of PNE SOLUTION Co., Ltd., and then at a constant voltage of 4.25V Charge once at a cut-off current of 5% relative to 1C, and then discharge to 3V at a constant current of 0.5C. This is regarded as 1 cycle, and this cycle is performed repeatedly.

When referring to FIG. 7 , it can be seen that while the porous inorganic separator of Comparative Example 1 started to deteriorate before 20 cycles, the porous separators of Examples 1 and 2 showed stable discharge capacity over longer cycles. The porous separators of Examples 1 and 2 were analyzed because they prevented dendrites for a longer time. In particular, it can be seen that when a porous separator using both a plate-shaped particle layer and a spherical particle layer is used as in Example 2, the dendrite prevention effect is more excellent and the discharge capacity is further improved.

Claims (8)

1. A porous membrane comprising: a porous layer comprising: a plurality of plate-shaped inorganic particles; and a first binder polymer positioned on a part or all of surfaces of the plate-shaped inorganic particles to connect and fix the plate-shaped inorganic particles, and a porous coating on at least one surface of the porous layer and comprising: a plurality of spherical inorganic particles; and on a part or all of the surfaces of the spherical inorganic particles to connect and fix the spherical inorganic particles the second binder polymer, Wherein in the porous layer, relative to the total weight of the inorganic particles in the porous layer, the content of the plate-shaped inorganic particles is 50% by weight or more; Wherein in the porous coating layer, the content of the spherical inorganic particles is 50% by weight or more relative to the total weight of the inorganic particles in the porous coating layer. 2. The porous separator according to claim 1, wherein the plate-shaped inorganic particles have an aspect ratio of 5 to 100. 3. The porous separator according to claim 1, wherein the plate-like inorganic particles comprise alumina, silica, zirconia, titania, magnesia, ceria, yttrium oxide, zinc oxide, iron oxide, barium oxide Titanium, alumina-silica composite oxide, or a mixture of two or more thereof. 4. The porous separator according to claim 1, wherein the spherical inorganic particles have an aspect ratio of 1 to 2. 5. The porous separator of claim 1, wherein the spherical inorganic particles comprise alumina, silica, or a mixture thereof. 6. The porous separator according to claim 1, wherein the porous layer further comprises spherical inorganic particles. 7. An electrochemical device comprising: positive electrode; negative pole; and a separator disposed between the positive electrode and the negative electrode, Wherein the membrane is a porous membrane according to any one of claims 1-6. 8. The electrochemical device according to claim 7, which is a lithium secondary battery.

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